Field of the Invention
The present invention relates to a cooling tank, in particular to a tank suitable for cooling rails in a thermal treatment plant of rail heads.
Background Art
Several solutions are known in the prior art for the thermal treatment of rolled rails, in particular aimed to obtain the hardening of the rail head.
Starting from a temperature higher than 600° C., rails are subjected to a quick cooling of the head either by the use of spray nozzles, which inject a cooling fluid (water, air or water mixed with air) on the rail head, or by the immersion of the head into a cooling tank containing a cooling liquid, for example water added with additive.
Compared to the solution with spray nozzles, the use of the tank allows to obtain a greater cooling uniformity, in the direction of the rail length, and higher cooling rates.
In order to further increase the thermal exchange inside the tank and thus speed up the treatment, some solutions of the prior art provide for jets of cooling liquid originating from holes located on the bottom of the tank and impinging the rail head immersed in the liquid: such jets increase the thermal exchange and accordingly the cooling rate.
Such a solution is described in document GB619699, which discloses a tank provided with three rows of holes on the bottom, wherefrom the cooling liquid exits, adapted to create jets of liquid directed towards the immersed rail head. However, the above document provides that the rail head to be treated rests on a support, which represents a hindrance for the liquid exiting from the holes and deviates it on the two sides of the rail head. As a result, the central zone of the rail head is not impinged by such jets and thus undergoes a non-uniform cooling.
Other solutions have been proposed to improve such cooling process, as disclosed for example in document JP63203724, which provide for supporting the rail by the bottom thereof so as to not have any hindrances between the jets and the immersed rail head and treat it as uniformly as possible.
In particular, JP63203724 provides for three separate jets, within the bath, directed onto the three faces of the rail head.
Another known solution is disclosed in document WO2010/133666A1 where a plurality of baskets occupies the upper part of the central volume of the tank, each basket comprising lower panels or deflectors and respective upper panels or deflectors. Lower and upper deflectors are reciprocally separated by a longitudinal element comprising a central plate provided with at least ten rows of nozzles and integrally fixed to two side plates. Said side plates are not coplanar with respect to the central drilled plate but are inclined downwards with respect to the plane defined by the central drilled plate by a predetermined angle, for example equal to 5÷15°. The lower deflectors are completely above the delivery manifold when the baskets are fully inserted into the tank modules. Together with the inner walls of the central volume, the lower deflectors define first compartments below the drilled central plate. At each of said first compartments there is provided a same number of calibrated holes, defining two opposite rows of nozzles respectively provided on two opposite sides of the underlying portion of the longitudinal stretches of the delivery manifold. At the junctions between the drilled central plate and non-drilled side plates, above the drilled central plate, there are provided curvilinear walls, convex with respect to the longitudinal center line plane of the module; and the upper deflectors, transversal to said curvilinear walls, together with said curvilinear walls, define second compartments above the drilled central plate.
A further known solution is disclosed in document US2009/200713A1 where two drilled plates are provided, with nozzles arranged on multiple rows which divide the cooling tank into three compartments, arranged one on top of the other.
However, in all these solutions of the prior art, at the exit of the nozzles, the jets of cooling liquid, going progressively up towards the rail, unavoidably tend to enlarge, loosing speed accordingly, and to flit about, i.e. to alternately direct rightwards or leftwards with respect to the hypothetical impact point, causing a non-symmetrical and non-uniform thermal transfer.
On the other hand, the rail head cannot be moved too close to the holes, located on the bottom of the tank, to preserve the treatment uniformity on the entire rail length and prevent the so-called “punctiform effect” which is due to the presence of a determined pitch between the holes: a rail too close to the holes is not uniformly treated along the longitudinal axis since the rail head zones, located perpendicularly above the holes, undergo a greater cooling than the stretches located at the pitch between two consecutive holes.
The need of providing a cooling tank that allows to overcome the above drawbacks is therefore felt.